Recently, demand for high technology and multifunctional properties of housing materials is increasing as large and light-weight products are becoming a widespread trend. In particular, as the appearance of molded products has become important, there is a need for a material which can provide scratch resistance and high grade texture at the same time, in addition to a flame retardant material having stability against fire.
One method for obtaining scratch resistance and flame retardancy at the same time is to alloy a polycarbonate (PC) resin and a (meth)acrylate resin, such as polymethyl methacrylate (PMMA).
The polycarbonate resin has good mechanical strength, transparency, thermal stability, self-extinguishing property, and dimensional stability so that it has been widely used in electrical and electronic products and parts of automobiles. Further, the polycarbonate resin can obtain flame retardancy even with a small amount of flame retardant, compared to a conventional polymer, since its chemical structure allows good flame retardancy. However, good scratch resistance cannot be obtained only with the polycarbonate resin since it has a low pencil hardness of 2B or so.
On the other hand, although polymethyl methacrylate resin has good scratch resistance and a high pencil hardness of 3H˜4H, it still has a disadvantage in that it can be difficult to impart sufficient flame retardancy to polymethyl methacrylate using conventional flame retardants.
Accordingly, a method of blending a PC resin and a PMMA resin has been suggested to improve both the scratch resistance and flame retardancy. However, although the PC resin and the PMMA resin are melt-kneaded at a high temperature, they may divide into separate phases due to their lack of compatibility. It is also very difficult for an alloy of PC and PMMA to be used in housings of electrical and electronic products. Due to the different refractive indices of the PC resin and the PMMA resin (1.59 and 1.49, respectively), the alloy of PC resin and PMMA resin may scatter light. This makes it difficult to provide color with high chroma, and a melt joining line is clearly shown during extrusion.
Korean Patent Publication Laid-open No. 2004-0079.118 discloses a method of lowering the molecular weight of polycarbonate during a kneading process using metal stearic acid ester in order to improve the compatibility between a polycarbonate resin and a (meth)acrylate resin. However, the method has a disadvantage in that a blend of the polycarbonate and the methacrylate resin has significantly low mechanical properties.
U.S. Pat. No. 4,027,073 discloses a method of coating the surface of a resin to improve scratch resistance. The method, however, requires an additional process step.